In this continuing study of the fetal myosin from skeletal muscle, the proposed research will be to determine whether the heavy chain of fetal myosin has a molecular weight slightly lower than that of the adult form. Labeled myosin prepared from fetal tongue in tissue culture will be purified and separated by electrophoretic techniques. Also antibodies to myosin from adult skeletal muscle, adult smooth muscle and non-muscle sources will be prepared. The monospecificity of each preparation will be determined and contaminating antibodies removed if necessary. These appropriate antibodies will be used to aid in the identity of the fetal myosin.